The present invention relates to a method and an apparatus for rapidly testing the wiring pattern of a printed circuit board on the basis of a negative pattern thereof obtained through a TV camera by detecting and picking up the image of a feeble fluorescent light emitted from a substrate (of glass epoxy, glass polyimide, etc.) of the printed circuit board.
There have been known heretofore apparatus developed for inspection of any defect in the pattern of a printed circuit board by the use of a TV camera as a pattern detector which detects a fluorescent light emitted from a substrate of the printed circuit board and picks up a negative pattern of the wiring pattern. Some of such prior apparatus are disclosed in, for example, U.S. patent application Ser. No. 619,918, abandoned, German patent application No. P3422395.9, and Papers Nos. 1682 and 1683 delivered in General Meeting of Electronic Communication Society, 1985. However, according to the above prior art in which two-dimensional image pickup by a TV camera is effected, it is impossible to achieve the pickup operation while keeping the printed circuit board in motion under continuous illumination. Therefore, in a state where an X-Y stage holding the printed circuit board thereon is repeatedly displaced by a predetermined distance and is brought to halt in a step-and-repeat mode, a still image of the wiring pattern is picked up and detected by the TV camera with the X-Y stage retained at a standstill.
In such pattern detection, the X-Y stage need not be halted in the case of using stroboscopic illumination. However, since its illuminance is relatively low, a stroboscope is not applicable as an illumination source. With regard to a means for solving the above problem, a superhigh-sensitivity TV camera with a SIT (silicone intensifier target) image tube may be employed as a pattern detector. But there still exists difficulty in its use due to the considerable amount of afterimage of the SIT image tube (30% afterimage remaining in the next scanning).